1. Technical Field
The present invention relates to a system for processing an MST function command in a numerical control system comprising a computerized numerical control apparatus (CNC) and a PMC (programmable machine controller), and more particularly to a system for processing an MST function command, which is especially capable of confirming a finish signal for an MST function at a high speed.
2. Background Art
In computerized numerical control (CNC) systems, an MST function command is issued from a computerized numerical control apparatus (CNC) and executed by a PMC (programmable machine controller). When the execution of the MST function is finished, a finish signal (FIN) is issued to continue the processing. The MST function collectively refers to an M function, an S function, and a T function.
One example of such a system is illustrated in FIG. 5 of the accompanying drawings Denoted at 31 is a processor in a computerized numerical control apparatus (CNC), 32 a common RAM, and 33 a processor in a PMC (programmable machine controller). In the computerized numerical control apparatus (CNC), a received MST function command is issued through the common RAM 32 to the processor 33. For example, a strobe signal MF and an M code signal of an M function are issued. The processor 33 in the PMC receives these issued signals, and executes the M function, after which a finish signal FIN is sent back to the processor 31 through the common RAM 32. The processor 31 then executes a next command. The processing in the computerized numerical control apparatus (CNC) and the PMC (programmable machine controller) is continued in the above manner.
FIG. 6 is a timing chart of a sequence for processing the M function in the computerized numerical control apparatus (CNC) and the PMC (programmable machine controller).
When the computerized numerical control apparatus reads an M function command, it issues an M code signal and, after a certain period of time, issues a strobe signal MF which is then received by the PMC to execute the corresponding M function. After completion of the M function, the PMC sends a finish signal FIN back to the computerized numerical control apparatus. In response to the signal FIN, the computerized numerical control apparatus removes the strobe signal MF and the code signal. The PMC removes the signal FIN upon confirmation of removal of the strobe signal MF. Upon confirmation of the removal of the signal FIN, the computerized numerical control apparatus reads and executes a next block. S and M functions can be processed in the same manner as described above with respect to the T function.
A conventional interface comprising relays has been employed to transmit and receive the finish signal FIN. Since this interface continues a sequence while confirming each signal from the transmitting terminal in view of chattering of the relays or the like, operation of the interface is time-consuming. The present system which transmits and receives signals through the RAM 32 between the computerized numerical control apparatus and the PMC as shown in FIG. 5 is thus wasteful of a long amount of time. In the PMC, for example, it is necessary to turn on the finish signal FIN, confirm the turning-off of the signal MF, and turn off the finish signal FIN. Processing the finish signal FIN takes about the same amount of time which is required to process three cycles of a control program in the PMC.
Inasmuch as one cycle of a normal PMC control program is processed in slightly less than 70 ms, the finish signal FIN is processed in about 200 ms. A program for a small-size numerically controlled lathe, numerically controlled automatic machine tool, or the like to process a single workpiece contains several tens of MST function commands. It requires about several seconds to several tens of seconds just to process finish signals for those MST function signals. This processing time is not negligible as compared with the overall machining time.